Impco model J fuel regulator and lockoff. Impco carburetor(s). I think carb model CA55 or CA100 should work fine. Very simple carbs. Very reliable system. Need more compression when running propane than when running gasoline. Your motor oil will never get dirty. You'll change it at the regular intervals and notice that at most it gets a little yellowish tint. Worked on forklifts for over 5 years. As the propane is evaporated by the heat from engine coolant running thru regulator, you need to have a way to bleed the air from the cooling system, or else, the regulator will ice up and engine will run poorly or not at all.
Aisan makes decent systems but they are terribly expensive, not as reliable as the Impco, and more complicated than the Impco. Also, they use a solenoid to effect fuel lockoff, thus requiring electrical connections. Impco uses engine vacuum.
If you shave the head and go with bigger valves, you can get good performance without using a turbo. Turbos are nice but not a low RPM proposition.
